The Institute of Electrical and Electronics Engineers (IEEE) has adopted a set of standards for wireless local area networks (LANs), known as 802.11. Wireless products satisfying 802.11a, 802.11b, 802.11g, and 802.11n are currently on the market.
A new generation of mobile and handheld devices has emerged under 802.11n, supporting multiple wireless interfaces or radios. A single mobile device, for example, may have three or four radios, each one supporting a different wireless network, such as wireless wide-area network, or WWAN (cellular), wireless local-area network, or WLAN (802.11a/b/g/n), wireless personal-area network, or WPAN (Bluetooth, UWB, Zigbee), and wireless metropolitan-area network, or WMAN (802.16). The flexibility built into such devices is intended to maximize wireless connectivity and user experiences.
A single basic service set (BSS) of a wireless local area network (LAN) may include an access point (AP) and a number of different stations (STA). The BSS may also be referred to as a cell. The WLAN may include a second BSS, a third, and so on. Entities in each BSS may communicate at any of a number of rates (known as the basic rate set). The entities of the BSS (the APs and STAs) communicate by sending frames to one another, whether through an AP or point-to-point between STAs.
FIG. 5 is a flow diagram of the synchronization engine of the adaptive receiver algorithm of FIG. 2, according to some embodiments; and
FIG. 6 is a flow diagram of the decoding engine of the adaptive receiver algorithm of FIG. 2, according to some embodiments.
Further, some wireless devices have multiple antennas at the transmitter and receiver, known as multiple-input-multiple-output (MIMO) systems. MIMO systems separate data for transmission into discrete cells and transmit the cells simultaneously over different antennas, but in the same frequency band, with the transmission channel, in essence, being treated as a matrix.
Typically, only limited orthogonal channels (typical 3 or 8) are available for transmitting between entities in the wireless network. Therefore, multiple cells that are simultaneously operated on the same channel cannot be separated far enough, and will interfere with one another. On the other hand, there may exist noise-limited environments, such as at a home office, where a single AP covers a large area, and signal strength on the edge is very weak, approaching the noise floor.
A technique known as maximum ratio combining, or MRC, is optimal for noise-limited environments. MRC attempts to maximize the strength of the received signal. Another technique, minimum mean square error (MMSE) filtering, is designed to minimize the received errors. MMSE results in a performance gain if the environment is interference-limited (as shown in FIG. 1). This performance gain is due to the capability of MMSE to suppress a dominant interfering source. However, MMSE consumes more power than MRC.
Thus, there is a need for a receiver that can dynamically switch between MRC and MMSE techniques, depending on the operating environment of the wireless device.